Conventional manufacturing methods such as the casting can only provide products with fixed configurations. If there is a need for improving material properties (strength and surface hardness for example) of the product to meet various requirements, a further relevant heat treatment can be applied so as to form a homogeneous internal texture or to provide a controllable surface. If the need is to modify the configuration of the object, then some specific manufacture methods can also be available already in the art.
The stacking-up layer or additive manufacturing method is a method for producing products with complicated configurations. Currently, among various additive manufacturing methods, powder bed fusion and direct energy deposition are two major application types of the metal additive manufacturing. The powder bed fusion of the additive manufacturing process comprises selective laser sintering (SLS), selective laser melting (SLM), direct metal laser sintering (DMLS), electron beam melting (EBM), and other relative techniques of powder bed fusion forming method. The direct energy deposition of the additive manufacturing process comprises laser engineering net shaping (LENS), laser metal deposition (LMD), 3D laser cladding, and other relative techniques of direct energy deposition forming method.
In all the aforesaid additive manufacture methods, during the solidification process, the phase change of the material between the solid state and the liquid state and the crystallizing mechanism may greatly be affected by the energy of the heating source (such as laser or electron beam) and the scanning speed. If provided energy is excessive, material may be vaporized. On the other hand, if provided energy is insufficient, the melting or sintering process is insufficient. In addition, while the scanning speed of the energy beams is too fast or too slow, quality of the additive manufacturing may be degraded. Therefore, optimal process parameters for the current additive manufacturing, or said as the stacking-up layer manufacturing, are limited in a specific range, and the crystallization (such as the crystal size and the crystal direction) of the material microstructure is usually uncontrollable by the variation of process parameters.